Xenoliths of lawsonite-ferroglaucophane rocks from a Quaternary volcano of Milos (Aegean Sea,Greece) |
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| Authors: | Christoph Hoffman Jörg Keller |
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| Institution: | Mineralogisches Institut der Universität, Alberstrasse 23b, D-7800 Freiburg/Br., W-Germany |
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| Abstract: | Xenoliths of metamorphic rocks with ferroglaucophane + albite + stilpnomelane + muscovite ± lawsonite ± pumpellyite are described fromn the rhylolitic tephra deposits of the Late Quaternary Phyriplaka Volcano, Milos, Aegean Island, Greece. The chemical bulk analyses reveal metabasaltic parent rocks with strongly modified chemical compositions. Unusual for common fresh basalt types is extreme Na2O combined with low K2O and rather low CaO. These are chemical characteristics of spilitic basalts. High iron in the bulk rock and very high Fe/Mg is probably the cause of extreme ferroglaucophane compositions. The metamorphic assemblages point to a high-p/low-T metamorphism in the pressure range 4–8 kb and with temperatures of about 350°C. Phyriplaka Volcano is likely to have only a shallow explosive center and ferroglaucophane rocks were ejected from the immediate basement of the island, which was uplifted after the metamorphic event. |
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